Potential-Tailored Aryl-Sodium Reagent with Moderate Ionic Binding Strength Enables Precise yet Fast Hard Carbon...

Hard carbon (HC) is a promising anode for sodium-ion batteries (SIBs), but coal-derived HCs often exhibit low reversible capacity and poor initial Coulombic efficiency (ICE) due to irreversible sodium (Na) loss on defective carbons. Presodiation can directly improve ICE, but the imprecise and slow process can lead to under- or oversodiation and the formation of thick and unstable byproducts. Here, we propose a high precision and fast presodiation by aryl-sodium (Ar-Na) compounds dissolved in tetrahydrofuran (THF) with controlled potential and Ar-Na binding energy. Based on the thermodynamic driving force (redox potential) and ionic transfer kinetics (Ar-Na binding strength), a dual-descriptor design principle for presodiation agent is established. Phenanthrene-sodium (Ph-Na) with a moderate ionic binding energy of - 0.92 eV and a matched redox potential of 0.24 V versus Na⁺/Na enables ∼100% ICE within 60 s and facilitates the formation of an ultrathin inorganic-rich SEI in the battery that enhances interfacial kinetics and cycling stability. The presodiated HC delivers a reversible capacity of 308.9 mAh g^-1, and paired with a Na₃V₂(PO₄)₃ (NVP) cathode exhibits 94.8% ICE, 99.2 mAh g^-1 discharge capacity, and 82.6% capacity retention after 350 cycles, demonstrating a scalable presodiation strategy for practical SIBs.